Automatic transmissions of the prior art, in particular for motor vehicles, comprise planetary gearset assemblies which are engaged by means of frictional or shift elements such as clutches and brakes and are usually connected to a starting element such as a hydrodynamic torque converter or a fluid clutch that can operate with some slipping action and is optionally provided with a bridging clutch.
Such a transmission is described in EP 0 434 525 A1. It comprises essentially a drive input shaft and a drive output shaft arranged parallel to one another, a dual planetary gearset assembly concentric to the drive output shaft, and five shift elements in the form of three clutches and two brakes, whose selective engagement, two at a time, determines the various gear transmission ratios between the drive input and drive output shafts.
Furthermore, from DE 199 495 07 A1 by the present applicant a multi-stage transmission is known, in which two non-shifting main gearset combinations are provided, which produce two rotation speeds on the output side which, besides the speed of the drive input shaft, can optionally be engaged with a shiftable dual planetary gearset assembly that acts on the drive output shaft, by selectively closing the shift elements used in such manner that to shift from one gear to the respective next gear up or down, only one shift element of the two shift elements actuated at the time has to be engaged or disengaged.
In addition, within the scope of EP 0 434 525 A1 a multi-stage transmission is disclosed, which contains a drive input shaft and a drive output shaft arranged in a housing, a planetary gearset assembly arranged concentrically with the drive output shaft consisting of four elements denoted as from the first to the fourth in the order of their speed, i.e. a so-termed double planetary gearset assembly, and five shift elements, namely three clutches and two brakes, whose selective actuation in pairs determines various transmission ratios between the drive input and drive output shafts, such that the transmission has two power paths which enable six forward gears to be engaged by the selective actuation of the five shift elements two at a time.
The purpose of the present invention is to propose a multi-stage transmission of the type described at the start, in which the structural elaboration is optimised and, in addition, the efficiency in the main gears is improved in relation to slippage and gearing losses.